1. Field of the Invention
The present invention relates to laser processing apparatus and laser processing methods. More particularly, the present invention relates to a laser processing apparatus and a laser processing method in which fine processings are performed with a laser beam while a processed surface is observed with a microscope.
2. Description of the Background Art
FIG. 1 is a vertical section of a conventional laser processing apparatus, and FIG. 2 is a diagram for describing a processing method in the case where glass is provided above a surface of an object to be processed in the conventional laser processing apparatus.
Referring to FIG. 1, the laser processing apparatus includes a microscope portion 1, a beam section forming device 2, an optical coupling device 3, a laser oscillator 4, a light source 5 and an observing portion 7. Microscope portion 1 constitutes a microscope of so-called infinite lens-barrel type, in which an objective lens 1b is attached to the lower end portion of lens-barrel 1a. A lens 1c for collimating light from a focal point outside the objective lens 1b and a lens 1d for converging the collimated light in turn are provided above objective lens 1b. Furthermore, in microscope portion 1, a first half mirror 1e is provided above lens 1d with an angle of approximately 45.degree. with respect to the optical axis of these lenses, and an observing portion 7 is provided on the right side of half mirror 1e in the drawing.
The upper end portion of lens-barrel 1a is opened, and the beam section forming device 2 is coupled thereto. Beam section forming device 2 is cylindrical-shaped as is lens-barrel 1a. The beam section forming device 2 includes a main body 2a provided on the upper end portion of lens-barrel 1a and a light shielding plate 2b provided in main body 2a perpendicular to the center axis of main body 2a. Light shielding plate 2b has an opening 2c at its central portion. Although not shown in the figure, the shape of opening 2c can be arbitrarily changed.
Optical coupling device 3 is coupled to the upper end portion of beam section forming device 2. Optical coupling device 3 includes a main body 3a, a second half mirror 3b, a collimator portion 3c and a correction plate 3d. Main body 3a is cylindrically shaped to correspond to main body 2a of the beam section forming device 2. Second half mirror 3b is provided inside main body 3a with an angle of 45.degree. with respect to the central axis of the main body 3a. Collimator portion 3c is provided on the left side of half mirror 3b for collimating the light from the light source 5, and correction plate 3d is provided above half mirror 3b. Laser oscillator 4 is coupled to the upper end portion of main body 3a, and laser beam r1 is emitted from a laser device 4a therein.
Furthermore, reference light r2 is emitted from an optical source 5 and is transmitted to collimator portion 3c through an optical fiber 5a. The laser beam r1 passes through correction plate 3d and second half mirror 3b. After collimation, the reference light r2 is reflected downward by the second half mirror 3b. Both the beam r1 and the reference light r2 follow a common optical path r. Light source 5 includes a tungsten halogen lamp and a film for changing white light produced by the tungsten halogen lamp into distinguishable monochromatic light.
In laser processing with a laser processing apparatus configured as described above, an object 6 to be processed is provided in the vicinity of objective lens 1b of microscope portion 6a which is 1 and a portion to be processed is optically enlarged and observed through observing portion 7. Next, a spot of reference light r2 is formed at the portion 6a to be processed changing the shape of opening 2c in the beam section forming device 2 while an operator observes the spot shape appearing on portion 6a with the microscope, allows the operator to select the spot shape needed for a desired processing. Subsequently, laser beam r1 is emitted from laser device 4a of laser oscillator 4. The emitted laser light r1 is thus converged as a spot having substantially same shape as the spot of the reference light on the portion 6a to be processed by the objective lens 1b, and the desired processings are performed.
In the conventional laser processing apparatus configured as described above, visible light is seen in the observation portion 7. The reference light r2 for irradiating the object 6 to be processed and indicating the spot shape is also visible light. On the other hand, if the laser light r1 used for processings is emitted from YAG or CO.sub.2 type laser device of laser light r1 is in the near infrared or far infrared range, respectively. If the chromatic aberration is corrected in the respective wavelength ranges in the optical system at the portion where visible light and laser beam pass through, there is no problem.
However, when objective lenses 1b, 1c have to be for use only for visible light, and when an object to be processed is a liquid crystal display, for example, a glass is provided above the electrode pattern as shown in FIG. 2, so that the light which passes through objective lenses 1b, 1c only for use for visible light forms an image at position P2 as shown by the broken line in FIG. 1 even if focusing on an electrode pattern as an object 6. This is because the refractive index of the laser beam r1 having long wavelength is made small. Accordingly, a precise processed shape cannot be formed on the surface of object 6.
In the case shown in FIG. 2, even if objective lenses 1b and 1c are capable of dual use for visible light and infrared light, even if focusing on the surface of object 6 with visible light, the focal point of the infrared light (i.e. the laser beam) is at P3 because of the presence of the glass plate 8 above the surface of object to be processed. The result is that a precise processed shape still cannot be formed on the surface of object 6.